1. Field of the Invention
This invention relates generally to rigid disk drives, and more particularly to rigid disk drives for pocket, palm-top, and laptop computers.
2. Description of Prior Art
The continuing trend toward smaller portable computers has created the need for a new class of miniature information storage devices. Portable applications for information storage devices have resulted in increasingly severe environmental and physical requirements. Small size, low power consumption, environmental endurance, low cost and light weight are characteristics that must co-exist in these applications; they cannot be met by simple extensions of previous technology.
Many examples of miniaturized reduced "footprint" disk drives have been described in patents such as U.S. Pat. No. 4,568,988 to McGinley, et al, issued Feb. 4, 1986, Reexamination Certificate (953rd), U.S. Pat. No. B14,568,988, certificate issued Nov. 29, 1988, U.S. Pat. No. 4,933,785, issued Jun. 12, 1990 to Morehouse, et al. The rigid magnetic recording disk utilized in the device, described in McGinley, et al., had a diameter of approximately 3.5 inches. In the Morehouse, et al. device described in that patent, the rigid disks utilized in the drive had a nominal diameter of 2.5 inches. The "footprint" (width by length measurement) of the drive described in the above-noted Morehouse, et al. patent was described as being 2.8 inches by 4.3 inches. That is, the housing used to enclose the rigid disk drive was 2.8 inches wide and 4.3 inches long. A rigid disk drive of that size is generally applicable to computers having a size of 8.5 inches by 11 inches by 1 inch. Another patent describing a relatively small diameter disk was issued Jun. 18, 1991 to Stefansky, U.S. Pat. No. 5,025,335. Stefansky describes a 21/2' form factor disk drive utilizing a single rigid disk having a diameter of approximately 2.6 inches. However, these products do not provide the combination of features needed for "pocket,""palm-top" and laptop computers.
History has shown that as disk drives become smaller and more efficient, new applications and uses for disk storage become practical. For example, using the disk drive as a circuit board assembly component requires further reduction in the physical size of the storage device as well as unique mounting strategies, issues addressed by this invention.
Use of disk drive storage devices in palm-top computers and small electronic devices, such as removable font cartridges for laser printers, require a level of vibration and shock resistance unobtainable with present large disk drives. These new applications require equipment to survive frequent drop cycles that result in unusually high acceleration and shock. It is well known that the force on an object is directly proportional to its mass, therefore reducing mass is an essential strategy for improving shock resistance.
Portable equipment also makes stringent demands on the durability and stability of the storage equipment under extreme dynamic, static, temperature and humidity stress. A device of small dimensions by its nature experiences less absolute temperature induced physical dimensional displacements. High humidity, especially during storage conditions, can aggravate a phenomenon known as "stiction" that occurs with conventional disk drives; the transducer head clings to the smooth disk surface, which can stall the spin motor and damage the heads.
The greater the power consumption, the larger and heavier the battery pack becomes. Hence, for a given operating time, power consumption is a primary and unavoidable design consideration for portable devices. In fact, the weight of a portable device is dependent on the total energy required to meet operational mission time. For disk drive equipment energy use is especially important during what is known as standby or power-down modes. Low power consumption also reduces parasitic heat, an important consideration in compact electrical equipment. Reducing the diameter and thickness of the information disk(s) can also provide significant reduction in power consumption during spin up. Modern disk drive power management methods use intelligent decision strategies, evaluating disk drive usage patterns to sequence power saving shut down features.
FIG. 24A is a block diagram of a prior art servo field 2400. The servo field 100 is the same length and includes, starting at its leading edge, a write splice sub-field 2401, an automatic gain control (AGC) sub-field 2402, a sector mark subfield 2403, an index sector identifier 2404, a defect bit 2405, a Gray code track number sub-field 2406, and a track position sub-field 2407 followed by another write splice sub-field. Servo field 2400 is preceded and followed by data regions 2410 and 2411, respectively. As explained more completely below, AGC sub-field 2402 is actually divided into two parts. The first part is a write-to-read transition zone and the second part provides the actual AGC data.
FIG. 24B is a flat view of the magnetic dibits in one servo field in tracks 3 to 6 of the disk. The other servo fields and data fields have the same general structure as illustrated by the block diagram of FIG. 24A. FIG. 24C is the signal pattern generated when the information in track 3 is read.
FIGS. 49A and 49B illustrate two- and three-disk embodiments of HDAs incorporating the prior art low-profile architecture. The spacing between adjacent disks 4920 is approximately two times the space t required for a read/write read, or 3.0 mm, to provide space for the two read/write heads 4930 and 4931 disposed between the adjacent disks. Thus, each additional disk 4920 increases the thickness of the prior art HDA by 3.6 mm (two spaces t and 0.6 mm for the thickness of the additional disk). Therefore, the thickness of the two-disk, four-head HDA of FIG. 49A is approximately 17.2 mm, and the thickness of the three-disk, six-head HDA of FIG. 49B is approximately 20.8 mm. Ferrite shields 4940 are illustrated in both FIGS. 49A and 49B.